Ionic liquids (ILs) comprise a specific class of molten salts composed of organic cations joined both to organic or inorganic anions. They have a strong chemical similarity to molten inorganic salts and the main difference is that they are liquid at room temperature, or conventionally below 100° C.
The chemical structure of ionic liquids allows for many combinations of anions and cations, making it feasible to obtain compounds with varied properties and which can be designed for a given application.
The diverse combinations between anions and cations also influence the physical-chemical properties of ionic liquids. In general, the type of anion determines more strongly the thermal stability and its miscibility in water. Examples of this latter property, which can be mentioned are hydrophilic anions (such as chloride and iodide), which grant miscibility to ILs in any proportion with water, while the PF6 anion limits the solubility of ILs in water.
On the other hand, the cation mainly influences properties such as viscosity, melting point and density, amongst others.
Recently, the study of the interfacial properties of ionic liquids has received a lot of attention. For a series of ionic liquids, it was observed that an interfacial behavior and aggregation behavior similar to those exhibited by the tensoactive agents of the cationic chain. See Bowlas, C. J. et al., Liquid-crystalline ionic liquids, CHEM. COMMUN., 14, pp. 1625-1626, 1996; and Holbrey, J. D. & Seddon, K. R. J., The Phase Behaviour of 1-alkyl-3-methylimidazolium tetrafluoroborates, J. CHEM. SOC., Dalton Trans., 13, pp. 2133-2139, 1999.
Due to the known tensoactive capacity of certain ionic liquids, one can conclude that ionic liquids are fluids with the potential to act as demulsifiers, or emulsion breakers, which are nothing more than tensoactive destabilizers of emulsions; and that the mixing of ionic liquids is a process resulting from both the length of the hydrocarbon chains of the cation and the nature and size of the anion.
Demulsifying chemical agents have been employed in the breakup of petroleum emulsions. The efficiency of this treatment depends on the viscosity of the medium as well as the stability of the emulsion, which in turn is influenced by the composition of the natural tensoactive agents, water content and concentration of salts, the distribution of the size of water droplets as well as experimental conditions such as temperature, age of the emulsion, etc.
For emulsions generated from heavy oils, these treatments have not been very efficient when more severe conditions are required for the destabilization of emulsions, in particular in terms of temperature, resulting in a high consumption of inputs and energy.
A recent technology is based on the application of radiation in the microwave range. Using microwave irradiation, it is possible to accelerate the heating up of petroleum emulsions, aiding the separation of the water-oil phases via thermal effects. In addition to this, it is believed that the microwaves interact with the polar types that make up the interfacial film, which protects the emulsionated droplets, hence encouraging non-thermal effects capable of modifying the conformation of tensoactive agents in the interface, hence favoring destabilization.
The article by Fortuny, M. et al., Effect of salinity, temperature, water content, and pH on the microwave demulsification of crude oil emulsions, ENERGY & FUELS, 21, pp. 1358-1364, 2007, constitutes one of the few investigations into the petroleum field which seeks to understand the effects of the characteristics of water/oil (W/O) emulsions on performance of treatment via microwave energy irradiation under controlled conditions.
The effect that the microwaves cause is based on the reorganization of the loads of polar molecules (polarization) and the free ions of the dielectric materials induced by the electric field of the radiation. This type of effect is known as dielectric heating and may be obtained by two classic mechanisms of interaction between microwaves and the material: the rotation of dipoles and ionic conduction.
Ionic liquids, as they are molten salts, have dielectric properties that favor their interaction with electromagnetic waves. ILs have a high capacity to absorb microwaves and subsequent transformation of this electromagnetic energy into heat. In fact, the constant dielectric of ionic liquids quantifies the capacity of the material to store electromagnetic energy. Hence, substances with constant high dielectrics tend to absorb microwave irradiations well.
Patent literature registers a small number of documents relating to microwave applications and ionic liquids in the field of water/oil emulsion treatment.
In international publication WO 2001/012289, a method is described to treat an emulsion which comprises water droplets in an organic liquid in order to separate the water and the organic liquid, in which the emulsion is subjected to microwave radiation at a frequency of 300 MHz to 100 GHz, in order to heat up the droplets selectively. At the frequency chosen, the droplets tend to transform the electromagnetic radiation into heat.
In U.S. Patent Application Publication No. 2008/0221226, from the same applicant, a method is described for the treatment of W/O emulsions with the help of microwaves in order to systematize a series of stages of the process intended to provide, for a crude oil, at least 90% emulsion treatment efficiency.
In international publication WO 2006/111712, the application of ionic liquids as surfactants in the stabilization of water/oil (W/O) or oil/water (O/W) emulsions and micro-emulsions is described. The ionic liquid employed as surfactant is a salt of a general formula (I) C+ A− which exists in a liquid state at a temperature of 150° C. and at least one of a cation C+ and an anion A− comprise a pendant hydrophobic group attached to an ionic head group, and A− represents an anion containing phosphorus or an alkyl sulfate anion of a general formula ROSO3− where R is an alkyl group with at least 8 carbon atoms.
In international publication WO 2006/131699 a process is described to break an emulsion of an ionic liquid which is a salt in a liquid state at a temperature lower than 150° C. and an oil, the process includes the phases of:                a) Irradiating the emulsion with microwave radiation;        b) Separating the emulsion in a phase comprising an ionic liquid and an oil phase; and        c) Recovering at least one of the phases.        
Emulsions including ionic liquids may be formed in processes in which this compound is used as an extractor agent of polyaromatic and sulfated compounds, or as a catalyst in organic reactions. In these processes, it is interesting to stimulate the swift separation of the phase comprising the ionic liquid for subsequent purification and re-use.
International publication WO 2007/138307 presents an extraction process for sulfated acid types of matrixes of crude petroleum or distillates of petroleum in which basic ionic liquids are used as extractor agents.
The basicity of the ionic liquid can be verified for specific functional groups incorporated in each cation and/or anion portion of the molecule.
Therefore, despite the range of documents available in literature, a treatment process for W/O emulsions in which separation is effective and at the same time with low energy consumption, is still necessary.
The process described below sets out the treatment of W/O emulsions in the presence of an ionic liquid which acts as a demulsifier and a heating source in which heating to enable the breaking of the emulsion is carried out using conventional thermal means or using radiofrequency energy such as microwaves. The application of ionic liquids as demulsifying agents is particularly useful when combined with microwave irradiation, enabling the aiming of microwave radiation at the W/O interface, favoring the destabilization of the protective film responsible for the stability of the emulsions.